1. Field of the Invention
The present invention relates to a vehicle headlamp for switching at least a first light distribution pattern, for example, a light distribution pattern for low beam (a light distribution pattern for passing) and a second light distribution pattern, for example, a light distribution pattern (a light distribution pattern for cruising) from each other to emit light forward of a vehicle.
2. Description of the Related Art
A vehicle headlamp of such type is conventionally known (for example, Japanese Unexamined Patent Application Publication No. 2010-108777). Hereinafter, a conventional vehicle headlamp will be described. The conventional vehicle headlamp is provided with a semiconductor-type light source, a fixed reflector, a movable reflector, a driving source, and a driving force transmission mechanism made of a rack and a pinion. Hereinafter, functions of the conventional headlamp will be described. When the movable reflector is positioned in a first location, if the semiconductor-type light source is lit, a light distribution pattern for low beam is obtained. When the movable reflector is positioned in a second location via the driving source and the driving force transmission mechanism, a light distribution pattern for high beam is obtained. In such a vehicle headlamp, it is important to maintain a load between the rack and the pinion of the driving force transmission mechanism at its required minimum level and to maintain the related positional precision in stop location (between the first location and the second location) of the movable reflector with high precision.
However, in the conventional vehicle headlamp, if a backlash between the rack and the pinion is set to “0”, the related positional precision is maintained at high precision due to influence of thermal expansion and shrinkage of the rack and the pinion, whereas the load between the rack and the pinion increases due to the thermal expansion. On the other hand, if the backlash between the rack and the pinion is set to be large, the load between the rack and the pinion can be maintained at its required minimum level, whereas the backlash further increases due to thermal shrinkage and then the related positional precision lowers.
In addition, in the conventional headlamp, it is important to ensure that an engagement state (condition) between the rack and the pinion of the driving force transmission mechanism is stabilized.
However, in the conventional vehicle headlamp, the rack rotates around a fixed center with respect to the driving source due to a vibration or actuation load at the time of, or subsequent to, assembling of the rack and the pinion of the driving force transmission mechanism, and then, the engagement state (condition) between a flat gear portion of the rack and a circular gear portion of the pinion may become unstable. In this case, a workload between the rack and the pinion of the driving force transmission mechanism increases, and there is a need to increase the driving source in size, or alternatively, there is a need to provide a mechanism for preventing the rotation of the rack. Due to an increase in size of the driving source or due to an increased number of parts such as the mechanism for preventing the rotation of the rack, its related manufacturing costs tends to become higher or its related mass or power consumption tends to increase.